In general, spray drying may be performed in many ways, and to all varieties it applies that the air distribution in the spray drying apparatus is one of the most vital parts. There are various systems depending on the plant design and the type of product to be produced. Different designs or adjustment of air dispersers are used in spray dryers to achieve either roughly a straight “plug-flow” air stream or a swirling air stream. The most common is that the air disperser is situated on top of the spray dryer ceiling, and the atomizing device(s) is/are placed at the middle of the air disperser thus ensuring an optimal mixing of the air and the atomized droplets.
Such air dispersers are provided in a variety of sizes and are traditionally manufactured by the use of assembly techniques including welding of components that are typically cut, cast, die-cast or formed by bending. Thus, a relatively large number of components need to be handled and connected to each other. The components include a set of guide vanes to be arranged in a guide vane framework which in turn is mounted in the space formed as a bowl-shaped structure to provide the distribution of drying air inside of the air disperser. Examples of prior art air dispersers incorporating such a framework are U.S. Pat. No. 4,227,896 (Niro) and WO 2007/071238 A1 (Niro). The guide vanes are normally welded to a nearby part or parts of the air disperser.
Although these air dispersers provide for reliable operation, the manner of manufacturing the air disperser is relatively cumbersome and entails some disadvantages due to in particular the assembly. In addition to the resources expenses, the manufacture of the individual components, each with a particular tolerance, and the subsequent assembly including the welding necessarily entail that deviations from a model configuration and from one air disperser to the other occur. In turn, the deviations lead to variations in the flow of drying air. This is particularly pronounced in smaller spray drying apparatus, in which the dimensions of the air disperser are small, and where the relative accumulated tolerances in apparatus manufactured by traditional techniques may be substantial.